The International Maritime Organization (IMO), as part of a policy of incrementally strengthening sulfur content restrictions in fuel oil in order to reduce sulfur oxides (SOx) contained in the exhaust gases of ships, has finally imposed a restriction of no more than 0.5% sulfur content, applicable to all sea areas. Therefore, ship operators need to take measures such as using low-sulfur-content fuel, or installing an exhaust gas processing device in the main engine, or the like.
A scrubber which reduces the concentration of harmful material in the exhaust gas by passing the exhaust gas through seawater is known as an exhaust gas processing device for a ship (see, for example, Patent Document 1 and Patent Document 2).
Patent Document 1: Japanese Patent Application Publication No. 2004-081933
Patent Document 2: Japanese Patent No. 2993891
As regards the amount of sea water supplied to the scrubber, an amount of seawater suited to the amount of sulfur oxide to be treated must be injected, and if an excessive amount of seawater is supplied, then there is a problem in that the pressure loss becomes greater, and the drive power of the seawater pump increases, whereas if the amount of seawater is insufficient, then there is a problem in that the concentration of sulfur oxides in the exhaust gas exceeds the limit value.
The present invention was devised in view of these circumstances, an object thereof being to provide an amount of seawater control device for a scrubber which is capable of achieving stable operation by supplying a suitable amount of seawater to the scrubber, in such a manner that the sulfur oxide concentration in the exhaust gas after processing never exceeds a limit value.
Furthermore, in the exhaust gas processing device disclosed in Patent Document 2, pH control is applied to the liquid bottoms of an absorption tower constituting a scrubber, and the exhaust gas is cleaned by recycling cleaning liquid from the bottom of the absorption tower. In general, a glass electrode system is used for a pH meter used in pH measurement, but a pH meter of this kind requires periodic cleaning and calibration, and it has been difficult to control the pH precisely on the basis of stable measurement results.
The present invention was devised in view of these circumstances, an object thereof being to provide an amount of alkali control device whereby it is possible to obtain a stable and highly reliable sulfur oxide removal rate, by applying alkali control of the seawater which is supplied to a scrubber, without using a pH meter.